Use of a microcrystalline polyamide to obtain a particular surface finish

ABSTRACT

The present invention relates to the use of a microcrystalline polyamide for obtaining an object having all or part of its outer surface formed from this microcrystalline polyamide and having a particular surface finish, in which:
         the manufacture of the object comprises steps carried out hot between the T g  (glass transition temperature) and the T m  (melting point) of this microcrystalline polyamide;   the transparency of the microcrystalline polyamide is such that the light transmission at 560 nm on a polished object 1 mm in thickness is greater than 80%, advantageously greater than 88%, the transparency being measured on the object obtained by standard processing methods, such as injection moulding and sheet extrusion/calendering.       

     Advantageously, the microcrystalline polyamide is such that its degree of crystallinity is greater than 10% and less than 30% (1st DSC heating according to ISO 11357 at 40° C./min) and the enthalpy of melting is greater than 25 J/g and less than 75 J/g (1st DSC heating according to ISO 11357 at 40° C./min). 
     Preferably, it such that its T g  (glass transition temperature) is between 40° C. and 90° C. and its T m  (melting point) is between 150° C. and 200° C. 
     Advantageously, it results from the chain-linking of monomers such that 50% or more, by weight, of these monomers are ≧C9 monomers (i.e. having a number of carbon atoms equal to 9 or higher).

This application is a divisional application of allowed U.S. patentapplication Ser. No. 11/158,650, filed Jun. 22, 2005. This applicationclaims priority of U.S. patent application Ser. No. 11/158,650 filedJun. 22, 2005, French Application No. 04.06757, filed Jun. 22, 2004 andU.S. Application No. 60/603,095 filed Aug. 20, 2004.

FIELD OF THE INVENTION

The present invention relates to the use of a microcrystalline polyamidein order to obtain a particular surface finish. More precisely, this isthe use of a transparent material of a particular type, which is solidbut malleable, particularly capable of reproducing the surface finishes(small-scale relief) and of being formed (large-scale relief, deeprelief) and of adhering to itself or to a substrate possibly withanfractuosities, all this with the purpose of producing an objectpossessing aesthetic, attractive and high-quality visual and tactileproperties and being resistant to mechanical, chemical and physicalattack.

This may concern a compression-moulded or injection-moulded bulk objectmade of this microcrystalline polyamide, or the outer layer completelyor partly covering an object. This outer layer may also be the outerlayer of a multilayer structure that covers a substrate. The structureis also called a film or sheet when its thickness is at most around 0.5to 1 mm. The structure consists of a single layer of a microcrystallinepolyamide or the multilayer structure that includes an outer (or upper)layer, that is to say the surface layer of the object, is fixed to theobject by any means. For example, the structure is placed in aninjection mould, the upper layer being placed on the mould wall side,and then the substrate in the melt state is injected on the oppositeside. The structure may be thermoformed before being placed in themould. After the mould has cooled down and been opened, the substratecovered with the structure is recovered.

The microcrystalline polyamides of the invention make it possible tohave an upper face that can easily render surface finishes or take agrain, that is to say is capable of becoming smooth and shiny (incontact with a sufficiently hot polished metal mould wall) or ofbecoming matt and grained (on contact with a sufficiently hot, matt orgrained, metal mould wall), or of assuming a brushed appearance. Whathas just been described is merely an illustration of the principle, butit would of course not be outside the scope of the invention if thetexturizing walls of the mould (or of any other texturizing device) aremade of a material other than metal. Furthermore, it is veryparticularly one of the major advantages of the invention, namely theability of our microcrystalline material to be capable of rendering verycomplex surface finishes of non-metallic materials, such as fabrics,paper, leather, wood, plants, etc. It is known that plastics are illsuited to rendering complex surface finishes. Either plastics are solidand too rigid to assume the relief sufficiently, or they are in theliquid state and adhere strongly to the surface, and it would then beimpossible, once the plastic has resolidified, to strip the latter fromthe texturizing wall (for example made of fabric). This is because it iswell known that plastics cannot in general be given very complex or veryattractive surface finishes. It is known that plastics are generallyregarded as materials of mediocre quality compared with moreconventional materials, such as metals, fabrics, wood, leather, etc.

BACKGROUND OF THE INVENTION

The invention is the use of a particular polyamide polymer materialcalled “microcrystalline” for the purpose of obtaining decorative andfunctional objects having aesthetic, attractive and high-quality visualand tactile properties.

It is also desirable for these visuo-tactile properties to be lastingwhen faced with mechanical (impact, scratching), chemical (solvent) andphysical (UV) attack. Typically the manufacture of the object comprisessteps carried out with the material hot, in particular between the T_(g)(glass transition temperature) and the T_(m) (melting point) of thismicrocrystalline polyamide. Typically, the use of the object (subsequentlife of the finished object) will be at a temperature below the T_(g) ofthis microcrystalline polyamide.

Among polymer materials, amorphous polymers have the advantage of beingtransparent. Besides this intrinsic aesthetic advantage, they make itpossible to protect and to bring out an underlying decoration. Amongthese amorphous polymers, mention may be made of PMMA, PC and amorphousPAs. The latter are of particularly high performance (EP 550 308 and EP725 101). However, while they are being processed in the melt, they havethe drawback of rapidly going into the solid state (owing to their highT_(g), namely 100-200° C.) as they are being cooled and are thereforeill-suited for faithfully retranscribing the surface finish and feel ofthe mould and, more generally, of a complex texturizing surface. Sincethey are typically very rigid and barely malleable below their T_(g),they are ill-suited to being formed in the solid state (for example bystamping). An amorphous polymer of low T_(g) (<60° C.) is itself barelyable to be envisaged, as it passes into the liquid state above itsT_(g), which of course makes it unsuitable for fulfilling its role ofprotecting the decorated object whenever the temperature rises somewhat.Another drawback of amorphous polymers, and even of amorphous PAs basedon high-carbon monomers (e.g.: PA-BMACM.1/12), is the inferior chemicalresistance (to stress cracking) and physical resistance (to UVradiation) compared with semicrystalline polymers, especiallysemicrystalline polyamides based on high-carbon monomers such as PA-11or PA-12.

Among polymer materials, semicrystalline polymers therefore have theadvantage of better chemical and physical resistance. Among these,semicrystalline polyamides constitute an advantageous choice. Amongsemicrystalline polyamides, preferred ones are those made fromhigh-carbon monomers, such as PA-11 and PA-12, since theirphysico-chemical resistance is even better, and their water uptake andthe consequences in terms of dimensional variations (and variations inother properties) are less than in the case of standard semicrystallinepolyamides such as PA-6 and PA-6,6. However, these semicrystallinepolyamides have the disadvantage of having a limited transparency and ofpassing rapidly into the solid state (owing to their fast and highrecrystallization rate) while they cool, and are therefore ill-suitedfor faithfully retranscribing the surface finish and feel of the mould.

We have discovered that the use of a particular polymer, namely a“microcrystalline” polyamide, in other words a transparent butnevertheless semicrystalline polyamide with a particular degree ofcrystallinity, can provide a particularly advantageous solution forobtaining decorative and functional objects having aesthetic, attractiveand high-quality visuo-tactile properties. The polyamides used in theinvention are those from semicrystalline polyamides that aremicrocrystalline, that is to say those consisting of crystallinestructures (spherulites) having a size small enough not to diffractlight and thus allowing good transparency. In the rest of the text,these will be referred to as “microcrystallines”. They may also becharacterized by a transparency such that the light transmission at 560nm on a polished object 1 mm in thickness is greater than 80%,advantageously greater than 88% (the object being obtained by standardprocessing methods, such as injection moulding and sheetextrusion/calendering).

This microcrystalline polyamide has many advantages. This is becausesuch a material does not have the drawbacks of:

-   -   low transparency;    -   solidifying too rapidly;    -   passing into the liquid state above its T_(g);    -   having a mediocre mechanical impact and scratch resistance;    -   having a mediocre chemical and stress-cracking resistance; and    -   having a mediocre UV resistance.

In fact, such a material has the key advantage of being easily formed bysolid-state (or partly solid-state) forming between its T_(g) and itsT_(m), thanks to its malleability in this temperature range. Theexpression “solid-state (or partly solid-state) forming” is understoodto mean various “warm” or “hot” thermomechanical treatments betweenT_(g) and T_(m), for the purpose of giving a finish possessing anaesthetic, attractive and high-quality and visuo-tactile character tothe polymer material (and to the object of which this polymer materialis one of the constituents).

We mention by way of examples of such solid-state forming the following:

-   -   passage from a 2D (two-dimensional) form, for example a 600 μm        sheet of the polymer material, to a 3D (three-dimensional) form        has the result of a step using a thermoforming or stamping        process between T_(g) and T_(m);    -   passage from one surface finish to another (smooth to rough),        typically by a step and a process of bringing the material into        contact with a textured surface (for example a rough metal or a        fabric), by compression moulding or overmoulding, between T_(g)        and T_(m), under pressure, for a certain time;    -   passage from a small-sized form (powder, small tile, sheet of        small area) to a larger form (bulk object, tiled surface),        typically by a sintering or welding process, between T_(g) and        T_(m), under pressure, for a certain time;    -   complexing, lamination, or assembling, for example of a 600 μm        sheet onto a substrate possessing anfractuosities (wood,        fabric), for example during a step of a coating or lamination        process;    -   complexing or transfer, for example onto a 600 μm sheet of the        polymer material, of fibrils or powder (whether pigmented or        not) for example during a step of a transfer process. This        process consists, for example, in bringing into contact, at a        temperature T between T_(g) and T_(m), under a pressure P, for a        time t, a sheet of polymer material with a substrate containing        the fibrils (e.g. a fabric), the said fibrils being transferred        from the substrate to the polymer material in which they will        become mechanically (and even also chemically) anchored, thereby        giving the material a particularly soft and warm feel. Another        example is that in which the polymer sheet is brought into        contact with a bed of polymer powder (e.g. PA-11) under similar        T, P, t conditions, all this giving us a material with a powder        feel;    -   superior mechanical resistance to impacts, knocks and scratches,        which resistance is most particularly manifested in terms of        little visual impact of the attack (no fraying, bleaching, etc.)        and not only in terms of weight loss or energy value;    -   hardness and non-malleability at T_(ambient) and at T<T_(g);    -   complete transparency, typically greater than or equal to that        of a conventional amorphous polymer such as polycarbonate (PC),        this being so for identical thicknesses of less than 2 mm;    -   chemical and stress-cracking resistance comparable to a        semicrystalline PA (e.g. PA-11);    -   excellent UV resistance; and    -   possibility of being decorated by sublimation (in addition to        more conventional techniques such as screen printing).

SUMMARY OF THE INVENTION

The present invention relates to the use of a microcrystalline polyamidefor obtaining an object having all or part of its outer surface formedfrom this microcrystalline polyamide and having a particular surfacefinish, in which:

-   -   the manufacture of the object comprises steps carried out hot        between the T_(g) (glass transition temperature) and the T_(m)        (melting point) of this microcrystalline polyamide;    -   the transparency of the microcrystalline polyamide is such that        the light transmission at 560 mm on a polished object 1 mm in        thickness is greater than 80%, advantageously greater than 88%,        the transparency being measured on the object obtained by        standard processing methods, such as injection moulding and        sheet extrusion/calendering.

Advantageously, the microcrystalline polyamide is such that its degreeof crystallinity is greater than 10% and less than 30% (1st DSC heatingaccording to ISO 11357 at 40° C./min) and the enthalpy of melting isgreater than 25 μg and less than 75 μg (1st DSC heating according to ISO11357 at 40° C./min).

Preferably, it is such that its T_(g) (glass transition temperature) isbetween 40° C. and 90° C. and its T_(m) (melting point) is between 150°C. and 200° C.

Advantageously, it results from the chain-linking of monomers such that50% or more, by weight, of these monomers are ≧C9 monomers (i.e. havinga number of carbon atoms equal to 9 or higher).

The term “microcrystalline polyamide” is also understood to meancopolyamides and compositions based predominantly on the latter, or inwhich the microcrystalline polyamide is the matrix constituent. Thesecompositions may be alloys, blends or composites, for examplecompositions that include plasticizers, stabilizers, pigments or dyes,mineral fillers and other miscible polymers that are compatible or havebeen made compatible by a third component.

The invention also relates to the objects manufactured from thismicrocrystalline polyamide and to the objects having, completely orpartly their outer surface made from this microcrystalline polyamideexhibiting a particular surface finish.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows schematically a representation of a DMA (dynamic mechanicalanalysis) plot in order to bring out the essential differences between,on the one hand, the microcrystalline polyamide of the invention and, onthe other hand, conventional amorphous polymers and semicrystallinepolymers.

In this FIG. 1:

PA-11 denotes the Atofina PA-11 called Rilsan BESN0 TL;amorphous PA denotes PA-BMACM.T/BMACM.1/2 obtained by the condensationof BMACM, the T (therephthalic) acid, the I (isophthalic) acid and the12 lactam, sold by Atofina under the name Cristamid® MS1700;μ-crystalline PA denotes a microcrystalline polyamide of composition, byweight:

-   -   65 parts of nylon-11 (PA-11) with an M _(w) of 45 000 to 55 000;    -   25 parts of IPDA.10/12 produced from the condensation of        isophoronediamine, the C10 (sebacic) acid and lauryllactam; and    -   10 parts of a block copolymer comprising PA-12 blocks of 5000 M        _(n), and PTMG blocks of 650 M _(n), the copolymer having an MFI        of 4 to 10 g/10 min (at 235° C./1 kg). This composition is        denoted in the rest of the text by PA-11 No. 6.

Plotted on this DMA graph on the x-axis is the temperature variable andon the y-axis the rigidity (modulus) variable. We can therefore see themodulus of the material over three broad temperature ranges, namelybelow T_(g), between T_(g) and T_(m), and above T_(m). Of course, we arenot interested in the region above T_(m), since all the materials areliquid and therefore cannot undergo solid-state forming. Of course,below T_(g) we are interested only in materials that are sufficientlyrigid for forming the structure of an object or for at least protectingthe object from mechanical stresses. We are therefore most particularlyinterested in the region between T_(g) and T_(m), the region wheretypically we envisage manufacturing the object or at least carrying outsome of the manufacturing steps, especially a finishing step, so as togive it the visuo-tactile properties that are desired.

In FIG. 1 we see that below T_(g) the three polymers are indeedsufficiently rigid (in order to protect the object during its use, andnot provide formability during manufacture of the object). Above itsT_(g), the amorphous PA becomes liquid: therefore it cannot be workedand formed in the solid state above its T_(g) and could not preserveintact its visual decoration (while below its T_(g) it is obviously muchtoo rigid and practically unmalleable to be worked and formed). Thesemicrystalline PA sees its modulus drop below T_(g), and it remains inthe solid state up to its T_(m). However, it is still too rigid to beeasily worked and formed in the solid state. The μ-crystalline PA is,between T_(g) and T_(m), sufficiently flexible and malleable to beeasily worked and formed in the solid state. However, between T_(g) andT_(m) the μ-crystalline PA is still sufficiently crystalline and rigidnot to flow or liquefy. The overall practical benefit of such a materialis therefore understood. In the case of the semicrystalline PA, theratio “cs/r” also represents, approximately, the degree ofcrystallinity, which is too high. In the case of the μ-crystalline PA,the ratio “cμ/r” also represents, approximately, the degree ofcrystallinity, which is just enough to be sufficiently solid and rigid,while still being sufficiently flexible and malleable in order to beeasily formed. If one were to imagine a still less crystalline material(having an even lower degree of crystallinity or enthalpy of melting),and therefore even less rigid between T_(g) and T_(m), this would thenbe faced with creep and flow problems, the product would no longer bemechanically durable and, from a practical standpoint, the behaviourwould be very close to that of an amorphous PA of the same T_(g).

In order to adjust the degree of crystallinity and therefore the modulusbetween T_(g) and T_(m), a person skilled in the art can vary therespective proportions of the various monomers or constituents. Toincrease the hot modulus of the polymer material, the proportion ofdisorganizing species, that is to say species that obstruct the regularorganization of the predominant macromolecules and therefore impedetheir crystallization, may be reduced. If on the contrary it is desiredto further reduce the modulus, this proportion would be increased.Depending on the intended final application, a fine adjustment maytherefore be made with regard to the level of malleability between T_(g)and T_(m), recognizing the fact that a less crystalline material willalso be less chemically resistant.

What T_(g) and what T_(m) should be chosen? The choice of T_(g) to T_(m)range corresponds as it were to the temperature at which the key stepsof manufacturing the finished article will be carried out. In manyindustrial processes, this temperature must remain reasonable, that isto say must not remain too high so that the other constituents of theobject do not undergo degradation (for example the liquefaction of anABS third polymer constituent, which liquefies at around 100° C.). It istherefore preferable to choose a T_(g) below 90° C. (but well above roomtemperature or above the service temperature of the object). Amicrocrystalline PA with a T_(g) of 140° C. for example would mean amanufacturing process (for manufacturing the final object) above 140°C., which may therefore be restrictive.

DETAILED DESCRIPTION OF THE INVENTION

By way of examples of microcrystalline polyamides, mention may be madeof the transparent composition comprising, by weight, the total being100%:

-   -   5 to 40% of an amorphous polyamide (B) that results essentially        from the condensation:        -   either of at least one diamine chosen from cycloaliphatic            diamines and aliphatic diamines and of at least one diacid,            chosen from cycloaliphatic diacids and aliphatic diacids, at            least one of these diamines or diacid units being            cycloaliphatic,        -   or of a cycloaliphatic α,Ω-aminocarboxylic acid,        -   or of a combination of these two possibilities, and        -   optionally of at least one monomer chosen from            α,Ω-aminocarboxylic acids or the possible corresponding            lactams, aliphatic diacids and aliphatic diamines;    -   0 to 40% of a flexible polyamide (C) chosen from copolymers        having polyamide blocks and polyether blocks, and copolyamides;    -   0 to 20% of a compatibilizer (D) for (A) and (B);    -   0 to 40% of flexible modifier (M);    -   with the condition that (C)+(D)+(M) is between 0 and 50%;    -   the balance to 100% of a semicrystalline polyamide (A).

This composition is microcrystalline. Without being tied by thisexplanation, the inventors believe that this is due to the very low sizeof the crystalline structures, the size being small enough not todiffract light as in the case of conventional semicrystalline polymers(PA-6, PA-12, PP, PE, PBT, etc.). However, this composition issemicrystalline since, as observed by DSC (“differential scanningcalorimetry”) analysis, the enthalpy of melting has a substantial valueof a similar order of magnitude as a nylon-11 (PA-11).

With regard to the semicrystalline polyamide (A), mention may be made of(i) aliphatic polyamides, which are products resulting from thecondensation of a ≧C9 aliphatic α,Ω-aminocarboxylic acid, of a ≧C9lactam or the products resulting from the condensation of an aliphaticdiamine and of an aliphatic diacid, at least one of the diamine and ofthe diacid being ≧C9.

By way of examples of aliphatic α,Ω-aminocarboxylic acids, mention maybe made of 11-amino undecanoic and 12-aminododecanoic acids. As examplesof lactams, mention may be made of lauryllactam. As examples ofaliphatic diamines, mention may be made of hexamethylenediamine,dodecamethylenediamine and trimethylhexamethylenediamine. As examples ofaliphatic diacids, mention may be made of adipic, azelaic, suberic,sebacic and dodecanedicarboxylic acids.

Among aliphatic polyamides, mention may be made by way of example andnon-limitingly, of the following polyamides: polyundecanamide (PA-11);polylauryllactam (PA-12); polyhexamethyleneazelamide (PA-6,9);polyhexamethylenesebacamide (PA-6,10); polyhexamethylenedodecanamide(PA-6,12); polydecamethylenedodecanamide (PA-10,12);polydecamethylenesebacanamide (PA-10,10) andpolydodecamethylenedodecanamide (PA-12,12).

Advantageously (A) is PA-11 and PA-12. It would not be outside the scopeof the invention if (A) were to be a blend of aliphatic polyamides.

With regard to the amorphous polyamide with a cycloaliphatic unit (B),the diamines are, for example, cycloaliphatic diamines containing twocycloaliphatic rings.

These diamines satisfy the general formula (I)

in which R1 to R4 represent identical or different groups chosen from ahydrogen atom or alkyl groups having from 1 to 6 carbon atoms, and Xrepresents either a single bond or a divalent group consisting of:

-   -   a linear or branched aliphatic chain having from 1 to 10 carbon        atoms;    -   a cycloaliphatic group having from 6 to 12 carbon atoms;    -   a linear or branched aliphatic chain having from 1 to 10 carbon        atoms, the said chain being substituted with cycloaliphatic        groups having from 6 to 8 carbon atoms;    -   a group having 8 to 12 carbon atoms, consisting of a linear or        branched dialkyl, with a cyclohexyl or benzyl group.    -   the cycloaliphatic diamines may be isomers of        bis(4-aminocyelohexyl)methane (BACM),        bis(3-methyl-4-aminocyclohexyl)methane (BMACM),        2,2-bis(3-methyl-4-aminocyclohexyl)propane (BMACP), and        para-aminodicyclohexylmethane (PACM). The other diamines        commonly used may be isophoronediamine (IPDA) and        2,6-bis(aminomethyl)norbornane (BAMN). The aliphatic diacids        were mentioned above. As an example, mention may be made of        PA-IPDA,12 that results from the condensation of        isophoronediamines with dodecanedicarboxylic acid. The amorphous        polyamide (B) may optionally contain at least one monomer or        comonomer chosen from:    -   α,Ω-aminocarboxylic acids;    -   aliphatic diacids;    -   aliphatic diamines;        these products were described above. As examples of (B), mention        may be made of PA-IPDA,10, coPA-IPDA,10/12, and PA-IPDA,12. It        would not be outside the scope of the invention if (B) were to        be a blend of several amorphous polyamides.

With regard to the flexible polyamide (C) and firstly the copolymershaving polyamide blocks and polyether blocks, these result from thecopolycondensation of polyamide blocks having reactive ends withpolyether blocks having reactive ends, such as, inter alia:

-   -   1) polyamide blocks having diamine chain ends with        polyoxyalkylene blocks having dicarboxylic chain ends;    -   2) polyamide blocks having dicarboxylic chain ends with        polyoxyalkylene blocks having diamine chain ends, obtained by        cyanoethylation and hydrogenation of aliphatic dihydroxylated        α,Ω-polyoxyalkylene blocks called polyetherdiols;    -   3) polyamide blocks having dicarboxylic chain ends with        polyetherdiols, the products obtained being, in this particular        case, polyetheresteramides. Advantageously, copolymers (C) are        of this type.

Polyamide blocks having dicarboxylic chain ends derive, for example,from the condensation of α,Ω-aminocarboxylic acids, of lactams or ofdicarboxylic acids and diamines in the presence of a chain-stoppingdicarboxylic acid.

The number-average molar mass M _(n), of the polyamide blocks is between300 and 15000 and preferably between 600 and 5000. The mass M _(n), ofthe polyether blocks is between 100 and 6000 and preferably between 200and 3000.

Polymers having polyamide blocks and polyether blocks may also includerandomly distributed units. These polymers may be prepared by thesimultaneous reaction of the polyether and polyamide-block precursors.

For example, it is possible to react a polyetherdiol, a lactam (or anα,Ω-amino acid) and a chain-stopping diacid in the presence of a smallamount of water. A polymer is obtained having essentially polyetherblocks and polyamide blocks of very variable length, but also thevarious reactants, having reacted in a random fashion, which aredistributed randomly along the polymer chain.

These polymers having polyamide blocks and polyether blocks, whetherthey derive from the copolycondensation of polyamide and polyetherblocks prepared beforehand or from a one-step reaction, have, forexample, Shore D hardnesses which may be between 20 and 75 andadvantageously between 30 and 70 and an intrinsic viscosity of between0.8 and 2.5 measured in meta-cresol at 25° C. for an initialconcentration of 0.8 g/100 ml. The MFIs may be between 5 and 50 (235°C., with a load of 1 kg).

The polyetherdiol blocks are either used as such and copolycondensedwith polyamide blocks having carboxylic ends or they are aminated inorder to be converted into polyetherdiamines and condensed withpolyamide blocks having carboxylic ends. They may also be mixed withpolyamide precursors and a chain stopper in order to makepolyamide-block polyether-block polymers having randomly distributedunits. Usually, these copolymers having polyamide blocks and polyetherblocks are those with PA-11, PA-12 or PA-6 polyamide blocks and PTMG(polytetramethylene glycol) or PPG (polypropylene glycol) polyetherblocks.

With regard to the flexible polyamide (C) consisting of a copolyamidethis results either from the condensation of at least one α,Ωaminocarboxylic acid (or a lactam), at least one diamine and at leastone dicarboxylic acid, or from the condensation of at least twoα,Ω-aminocarboxylic acids (or their possible corresponding lactams or ofa lactam and of the other in the form of an α,Ω-aminocarboxylic acid).These constituents are already described above.

By way of examples of copolyamides, mention may be made of copolymers ofcaprolactam and lauryllactam (PA-6/12), copolymers of caprolactam,adipic acid and hexamethylenediamine (PA-6/6,6), copolymers ofcaprolactam, lauryllactam, adipic acid and hexamethylenediamine(PA-6/12/6,6), copolymers of caprolactam, lauryllactam,11-aminoundecanoic acid, azelaic acid and hexamethylenediamine(PA-6/6,9/11/12), copolymers of caprolactam, lauryllactam,11-amino-undecanoic acid, adipic acid and hexamethylenediamine(PA-6/6,6/11/12), and copolymers of lauryllactam, azelaic acid andhexamethylenediamine (PA-6,9/12). The preferred copolyamides arecopolyamides with a pronounced copolymer character, that is to say withessentially equivalent proportions of the various comonomers, whichresults in properties furthest away from the corresponding polyamidehomopolymers. It would not be outside the scope of the invention if (C)were to be a blend of several copolymers having polyamide blocks andpolyether blocks, or a blend of several copolyamides or any combinationof these options.

With regard to the compatibiliser (D) for (A) and (B), this is anyproduct that lowers the temperature needed to make the blend of (A) and(B) transparent. Advantageously, this is a polyamide. For example, if(A) is PA-12, then (D) is PA-11. Preferably, this is a catalysedaliphatic polyamide.

With regard to the catalysed polyamide (D), this is a polyamide asdescribed above in the case of (A), but containing a polycondensationcatalyst such as a mineral or organic acid, for example phosphoric acid.The catalyst may be added to the polyamide (D) after it has beenprepared by any method, or, quite simply, and preferably, this may bethe rest of the catalyst used for its preparation. The term “catalysedpolyamide” means that the chemistry will be continued beyond the stepsof synthesizing the base resin and therefore during the subsequent stepsin the preparation of the compositions of the invention. Verysubstantial polymerization and/or depolymerization reactions may takeplace during the blending of the polyamides (A) and (B) and (D) in orderto prepare the compositions of the present invention. Typically, theApplicant believes (without being tied down to this explanation), thatpolymerization (chain extension) and chain branching (for example,bridging via phosphoric acid) continue to take place. In addition, thismay be considered as a tendency toward re-equilibration of thepolymerization equilibrium, and therefore a kind of homogenization.However, it is recommended that the polyamides be thoroughly dried (andadvantageously the moisture content properly controlled) in order toprevent any depolymerization. The amount of catalyst may be between 5ppm and 15000 ppm of phosphoric acid with respect to the resin (D). Forother catalysts, for example boric acid, the contents will be differentand may be chosen appropriately, according to the usual techniques forthe polycondensation of polyamides.

With regard to the flexible modifier (M), mention may be made, by way ofexample, of functionalized polyolefins, grafted aliphatic polyesters,copolymers having polyether blocks and polyamide blocks, theseoptionally being grafted, copolymers of ethylene with an alkyl(meth)acrylate and/or with a vinyl ester of a saturated carboxylic acid.The copolymers having polyether blocks and polyamide blocks may bechosen from those mentioned above in the ease of (C) preferably flexiblecopolymers being chosen, that is to say those having a flexural modulusof less than 200 MPa.

The modifier may also be a polyolefin chain with polyamide or polyamideoligomer grafted species; thus, it has affinity with polyolefins andwith polyamides.

The flexible modifier may also be a block copolymer having at least oneblock compatible with (A) and at least one block compatible with (B).

As examples of flexible modifiers, mention may also be made of:

-   -   copolymers of ethylene with an unsaturated epoxide and        optionally with an ester or an unsaturated carboxylic acid salt        or with a vinyl ester of a saturated carboxylic acid. These are,        for example, ethylene/vinyl acetate/glycidyl (meth)acrylate        copolymers or ethylene/alkyl        (meth)acrylate/glycidyl-(meth)acrylate copolymers;    -   copolymers of ethylene with an unsaturated carboxylic acid        anhydride and/or with an unsaturated carboxylic acid that can be        partly neutralized by a metal (Zn) or an alkaline metal (Li) and        optionally with an ester of an unsaturated carboxylic acid or        with a vinyl ester of a saturated carboxylic acid. These are,        for example, ethylene/vinyl acetate/maleic anhydride copolymers        or ethylene/alkyl (meth)acrylate/maleic anhydride copolymers or        else ethylene/Zn or Li (meth)acrylate/maleic anhydride        copolymers; and    -   polyethylene, polypropylene, ethylene-propylene copolymers,        these being grafted or copolymerized with an unsaturated        carboxylic acid anhydride and then condensed with a monoaminated        polyamide (or a polyamide oligomer). These products are        described in EP 342 066.

Advantageously, the functionalized polyolefin is chosen fromethylene/alkyl(meth)acrylate/maleic anhydride copolymers, ethylene/vinylacetate/maleic anhydride copolymers and ethylene-propylene copolymers,in which propylene is predominant, these copolymers being grafted bymaleic anhydride and then condensed with a monoaminated polyamide 6 ormonoaminated oligomers of caprolactam.

Preferably, this is an ethylene/alkyl (meth)acrylate/maleic anhydridecopolymer comprising up to 40 wt % of alkyl (meth)acrylate and up to 10wt % of maleic anhydride. The alkyl(meth)acrylate may be chosen frommethyl acrylate, ethyl acrylate, n-butyl acrylate, isobutyl acrylate,2-ethylhexyl acrylate, cyclohexyl acrylate, methyl methacrylate andethyl methacrylate.

As examples of grafted aliphatic polyesters, mention may be made ofpolycaprolactone grafted with maleic anhydride, glycidyl methacrylate,vinyl esters or styrene. These products are described in Application EP711 791.

It is recommended to choose a flexible modifier that does not reduce thetransparency of the compositions. The advantage of the compositions(A)+(B), (A)+(B)+(C) and (A)+(B)+(C)+(D) mentioned above is that theyhave a resulting refractive index close to most of the modifiers (M)mentioned. It is therefore possible to add a modifier (M) with the same(or very similar) refractive index. This was not the case with thetransparent polyamide compositions cited in the prior art, since theirrefractive indices are typically higher than the refractive index of themost usual modifiers (M).

In general, the modifier (M) is useful for further softening, or forconferring a particular property (hence being called a modifier) withoutthereby losing the advantageous properties of transparency,low-temperature manufacture and sublimation capability. Among theseadditional properties that the modifier may provide, we mention thefollowing: an impact modifier for improving the impact resistance; amodifier carrying reactive functional groups in order to improve theadhesion of the material to substrates; a modifier for giving a mattappearance; a modifier for giving a silky or slippery feel; a modifierfor making the material more viscous, so as to process it by blowmoulding.

It is advantageous to blend the modifiers so as to combine theireffects.

Advantageous compositions are those whose proportions of theconstituents are the following (the total being 100%) and are describedin Table 1 below:

TABLE 1 A B C + D + M C D M balance to 5 to 40 0 to 50 0 to 40 0 to 20 0to 40 100% balance to 20 to 30 0 to 50 0 to 40 0 to 20 0 to 40 100%balance to 5 to 40 0 to 30 0 to 30 0 to 20 0 to 30 100% Balance to 10 to30 0 to 30 0 to 30 0 to 20 0 to 30 100% balance to 20 to 30 0 to 30 0 to30 0 to 20 0 to 30 100% balance to 10 to 30 0 to 20 0 to 20 0 to 20 0 to20 100% balance to 10 to 30 5 to 15 0 to 15 0 to 15 0 to 15 100% balanceto 20 to 30 0 to 20 0 to 20 0 to 20 0 to 20 100% balance to 20 to 30 5to 15 0 to 15 0 to 15 0 to 15 100%

These compositions are manufactured by melt-blending the variousconstituents (in a twin-screw, BUSS® or single-screw extruder) usingstandard techniques for thermoplastics. The compositions may begranulated, for subsequent use (it is sufficient to remelt them) or elsethen injection-moulded in a mould or an extrusion or coextrusion devicefor manufacturing sheet or film. A person skilled in the art can readilyadjust the compounding temperature in order to obtain a transparentmaterial; as a general rule, it is sufficient to increase thecompounding temperature, for example to about 280 or 290° C.

These compositions may include thermal stabilizers, antioxidants and UVstabilizers.

By way of example of microcrystalline polyamides, mention may be made ofthe transparent composition comprising, by weight, the total being 100%:

-   -   5 to 40% of an amorphous polyamide (B) that results essentially        from the condensation of at least one optionally cycloaliphatic        diamine, of at least one aromatic diacid and optionally of at        least one monomer chosen from:        -   α,Ω-aminocarboxylic acids,        -   aliphatic diacids,        -   aliphatic diamines;    -   0 to 40% of a flexible polymer (C) chosen from copolymers having        polyamide blocks and polyether blocks, and copolyamides;    -   0 to 20% of a compatibilizer (D) for (A) and (B),    -   (C)+(D) is between 2 and 50%;    -   with the condition that (B)+(C)+(D) is not less than 30%,        the balance to 100% of a semicrystalline polyamide (A).

It differs from the previous one essentially by the nature (B) and to alesser extent by the proportions of the constituents. It is prepared inthe same way and is microcrystalline.

Advantageously, the proportion of (B) is between 10 and 40%, andpreferably between 20 and 40%. Advantageously, the proportion of (C)+(D)is between 5 and 40%, and preferably 10 and 40%.

With regard to the amorphous polyamide (B) in this othermicrocrystalline polyamide composition, this essentially results fromthe condensation of at least one optionally cycloaliphatic diamine andof at least one aromatic diacid. Examples of aliphatic diamines werementioned above; the cycloaliphatic dimities may be isomers ofbis(4-aminocyclohexyl)methane (BACM),bis(3-methyl-4-aminocyclohexyl)methane (BMACM), and2,2-bis(3-methyl-4-aminocyclohexyl)propane (BMACP). Other commonly useddiamines may be isophoronediamine (IPDA) and2,6-bis(aminomethyl)norbornane (BAMN). As examples of aromatic diacids,mention may be made of terephthalic (T) and isophthalic (I) acids.

The amorphous polyamide (B) may optionally contain at least one monomerchosen from:

-   -   α,Ω-aminocarboxylic acids,    -   aliphatic diacids,    -   aliphatic diamines,        these products were described above.

As examples of (B), mention may be made of the amorphous semi-aromaticpolyamide PA-12/BMACM, TA/BMACM,IA synthesized by melt polycondensationusing bis(3-methyl-4-aminocyclohexyl)methane (BMACM), lauryl-lactam(L12) and isophthalic acid and terephthalic acid (IA and TA). It wouldnot be outside the scope of the invention if (B) were to be a blend ofseveral amorphous polyamides.

Various embodiments will now be described.

A process in which the microcrystalline polyamide is particularlyadvantageous is overmoulding with in-mould decoration (IMD). Thismicrocrystalline polyamide material is particularly suitable for its usein the IMD process. This process consists in placing, in the bottom ofthe mould, a sheet or film that has been decorated beforehand (and,optionally, has been thermoformed beforehand) and in then inovermoulding (it would be more appropriate to employ the term“undermoulding”, but usually the term “overmoulding” is employed) apolymer in order to give substance to the object, the sheet or film thenbecoming the decorated surface of the object. The microcrystallinepolyamide is particularly suitable as it allows not only visual“in-mould” decoration but also tactile decoration by its ability to takeon the texture of the surface of the mould. The microcrystallinepolyamide, which is semicrystalline but not excessively crystalline, isin fact particularly suitable for sublimation decoration between itsT_(g) and its T_(m), (and preferably close to its T_(m)): thesublimation pigments easily penetrate into the material owing to thehigh mobility of its amorphous phase (and to the high proportion of thelatter) without thereby the material liquefying in its entirety andtherefore without the object deforming unacceptably. Among the otheradvantages of our microcrystalline polyamide, we stress its betterthermoformability (thermoforming often being employed beforeovermoulding), its much better chemical resistance than amorphouspolymers (for example, polycarbonate ABS) and its excellent resistanceto mechanical attack and to UV radiation (much better than that ofpolycarbonate). It goes without saying that the process for decoratedand overmoulded film is merely one example and that our microcrystallinepolyamide is advantageous for other manufacturing processes, such ascompression moulding, injection moulding, thermoforming and any processin which the ductility and malleability of the material is an asset, itbeing understood that the said process is carried out at least partly ata temperature between T_(g) and T_(m) (and it being understood thatsubsequently the service temperature of the object will be below thisT_(g), or that this T_(g) is substantially above room temperature).

“Solid-state paint”: advantage of the microcrystalline polyamide and ofthe IMD process as regards paint.

Up until now we have described the advantages of our material and itsapplications compared with amorphous or conventional semicrystallinepolymers. We will now compare it with objects that are decorated andprotected, not by polymers but by paint. Paint or screen-printing inkhas the advantage of being able to give not only aesthetic visualeffects but also attractive tactile effects. However, paint has thedrawback of requiring an often lengthy application process and thepresence of solvents, which from the ecological standpoint isundesirable. In terms of mechanical and chemical protection, paints, forexample those based on polyurethane, are not as effective as a coatingmade of a microcrystalline polyamide. Between its T_(g) and its T_(m),the microcrystalline polyamide is particularly flexible and malleable,while still remaining in the solid state. Its solid state allows it topreserve the integrity of its visual decoration (for example a sublimeddecoration−paint is obviously liquid during its application) and itsmalleability allows it to be easily applied to the substrate and toacquire an attractive surface finish and feel. Once applied, somewhat inthe manner of paint, the microcrystalline PA hardens and the decoratedobject is then effectively protected (the temperature is then belowT_(g)).

Grained visuo-tactile structure. A smooth shiny sheet ofmicrocrystalline PA is placed against a metal surface provided with agrained relief, the whole assembly being at 110° C., i.e. between T_(g)and T_(m), under 20 bar for 3 minutes. The PA-11 No. 6 composition(which has a T_(g) of about 55° C. and a T_(m) of about 188° C.) may beused for example. The sheet of microcrystalline PA has the advantage ofacquiring a surface relief, a visual appearance and a feel that are veryfaithfully reproduced. It is therefore possible, starting with the sameobject made of this microcrystalline PA, to give it subsequently adesired visuo-tactile effect, without any choice restriction andconsistent with the requirements of its final function (for example, todelustre glazing, to give a bottle a soft feel, etc.). Another advantageis that this texturing based on a visuo-tactile effect may be givenduring the final step in the manufacture of the object, in a “finishing”operation, and only on part of the surface of the object. What is more,the texture or decoration of the said object will be highly resistantthereafter (for example, resistant to scratching), during use of theobject (at T<T_(g)), the material hardening under the effect of time andan annealing operation.

With a conventional semicrystalline PA (e.g. PA-11), the reproduction ofthe relief is much less pronounced (the product being insufficientlydeformable between its T_(g) and its T_(m)); the mechanical resistance(for example scratch resistance) of the surface is also lower. With anamorphous PA (e.g. PA-BMACM.12), if T>T_(g), the PA object melts, whichis undesirable; if T<T_(g), the PA is marked very little (the product istoo undeformable and too rigid).

It is possible to use another process, that of overmoulding. A smoothbilayer sheet consisting of microcrystalline polyamide material/maleicanhydride-grafted polypropylene, is placed in the bottom of a grainedmould at 60° C., with the PA face on the grained mould side. This mouldis a mould of an injection moulding machine. An overmoulding operationis then carried out by injecting molten PP at 210-230° C. with a holdpressure of 500 bar. After removal from the mould, the surface on thesheet side has perfectly acquired the grained relief of the mould, As anexample of this bilayer material, it is possible to use PA-11 No.6/Orevac® 18729.

Corrected/polished visuo-tactile structure. A smooth and shiny sheet ofmicrocrystalline PA is now placed against a metal surface provided witha polish and with a high gloss, the whole assembly again being under thesame conditions (at 110° C., 20 bar for 3 to 5 minutes). Once themicrocrystalline PA sheet has cooled, it has a polish and a gloss betterthan the original, the several surface imperfections (small bumps and/orreliefs) being erased and smoothed out. The surface appearance of theproduct is therefore as it were easily “correctable”, this is not thecase with conventional semicrystalline PAs (e.g. a PA-11) or amorphousPAs (e.g. PA-BMACM.12). One advantage is therefore that it is possible,for example, to produce a sheet of microcrystalline polyamide withoutany particular precaution as regards the surface appearance. It maytherefore be manufactured at high speed and high productivity(extrusion, casting or blown-film processes). The surface appearancewill in any case be “corrected” by one (or more) subsequent finishingoperations, as described at the start of this paragraph.

It is possible to use another process, that of overmoulding. A smoothbilayer sheet consisting of microcrystalline polyamide material/maleicanhydride-grafted polypropylene, is placed in the bottom of a polishedmould at 60° C., with the PA face on the polished mould side. This mouldis a mould of an injection moulding machine. An overmoulding operationis then carried out by injecting molten PP at 210-230° C. with a holdpressure of 500 bar. After removal from the mould, the surface on thesheet side has perfectly acquired the polish of the mould. As an exampleof this bilayer material, it is possible to use PA-11 No. 6/Orevac®18729.

Double-sided visuo-tactile structure, with wood appearance & bonding onthe lower face and wood feel on the upper face. A smooth, shiny sheet ofmicrocrystalline PA is now placed against a wooden surface at a highenough temperature (but always within the T_(g)-T_(m) range) in such away that there is adhesion between the wood and the PA (the PApenetrating the anfractuosities of the wood surface, thus creatingmechanical anchoring). At the same time (or afterwards), a wooddecoration (made of wood or reproduced on a metal surface) is placed onthe other face at a temperature T that is low enough (but still withinthe T_(g)-T_(m), range) for there to be no adhesion but neverthelessthere is transfer of the surface texture. This therefore has theadvantage that the wood is protected by a PA surface (providingchemical, mechanical and UV resistance) and the advantage that this PAsurface has the texture and feel of wood. As an example, the operationmay be carried out as follows: the wood is bonded to one side of thesheet at 110° C. under 20 bar for 5 minutes and a metal plate with a“wood” graining is placed on the other side of the sheet, at the sametime (at 110° C., under 20 bar and for 5 minutes), the graining beingtransferred into the sheet.

Fabric visuo-tactile structure. A smooth shiny sheet of microcrystallinePA is now placed against a non-woven textile surface (for example at110° C., under 20 bar for 5 minutes). As described above, the surfacefinish of the non-woven will be faithfully retranscribed but also, if Tis high enough, but still within the T_(g)-T_(m) range, textile fibrilswill remain trapped in the sheet of microcrystalline PA, thereby givinga particularly pronounced soft feel, of the fabric type.

The fabric may be replaced with a bed of powder or a substrateimpregnated with powder, for example PA-11 powder. The hot contactingoperation is carried out between T_(g) and T_(m) under a pressure P fora time t, and a material with a “powder” feel is obtained. In additionto the feel effect, the powder and fibrils may be coloured or pigmented,which will give an additional visual effect. It is also possible toreplace the fabric with a bed of glass beads, therefore obtaining adifferent feel and even better scratch resistance.

Fabric visuo-tactile structure without impregnation. We now consider theease in which the texturizing surface is no longer a “non-woven” asabove, but a much less tearable fabric, or a textured paper, or a subtlyembossed leather surface, or another soft, finely porous texturizingsurface. In this case, we obtain very good and faithful retranscriptionof this subtle surface finish, without at all the particles of thetexturizing surface remaining trapped in our polymer material. Ourmaterial is sufficiently malleable and flexible for the surface reliefof the texturizing surface to be well “transferred”, but it is howeversufficiently solid and rigid not to bond excessively to the latter. Soas to obtain the desired effect and to control the desired degree ofadhesion to the texturizing surface or the substrate, the followingparameters may be varied: composition of the microcrystalline polyamide,which allows the degree of crystallinity to be varied (the lower thecrystallinity, the higher the adhesion); the thickness of themicrocrystalline polyamide sheet (the thinner the sheet, the greater theadhesion); the processing temperature (the higher the temperature thegreater the adhesion); the processing time (the longer the time, thegreater the adhesion); the processing pressure (the higher the pressure,the greater the adhesion).

We now no longer compare our material with a liquid of the paint type,but with a liquid of the polymer melt type. If the polymer melt isbrought into contact with a woven or non-woven or paper surface (anytype of readily porous surface), for the same objective of finallygiving the plastic an appearance and feel similar to that of thistexturizing surface, there will be the problem that the polymer meltadheres too strongly. It will then be impossible to remove the fabrictexturizing surface without damage. The latter will tear and/or willremain partly stuck to the plastic. In either case, we will not obtainthe desired feel.

Adhesion/weldability. A smooth shiny sheet of microcrystalline PA is nowplaced so as to be partly superposed on another sheet ofmicrocrystalline PA. The combination is pressed at a temperature Tbetween T_(g) and T_(m) (for example 180° C., under 30 bar for 3minutes). The material has the double advantage of being weldable and ofthe fact that this weld has almost the same thickness as the sheet(thanks to the flexibility and hot workability of this microcrystallinematerial).

Adhesion/sintering. Better sinterability of a microcrystalline polyamidepowder. Sintering is an operation that consists in consolidating powderby heating it below its T_(m). Ceramics are typically manufactured bysintering. This sinterability is to be combined with the weldabilitydescribed in the previous paragraph. More generally, themicrocrystalline polyamide of the invention possesses betterinterdiffusability between T_(g) and T_(m), that is to say two objects(for example, powder grains and sheets) brought into contact with eachother between T_(g) and T_(m) will be better able to be bonded together.Since the material of comparison is at a temperature between T_(g) andT_(m), it is by default a semicrystalline material (an amorphousmaterial, not having a T_(m), would be in the liquid state above itsT_(g)).

Malleability/any hot forming between T_(g) and T_(m). In general,malleability is better between T_(g) and T_(m), i.e. better formabilitybetween T_(g) and T_(m). For example, if a flat sheet of themicrocrystalline polyamide of the invention is placed, between T_(g) andT_(m), in a mould having a bowl shape, less force will have to be usedto force the material to adopt this bowl shape. Compared with theability to take a grain (see the previous paragraphs) forming is not sodifferent—at the end of the day this may be seen as a simple change ofscale between the grained surface, which is a relief on a small scale(hollows and bumps around one hundred microns in size), and the bowl,which is a relief on a large scale (tens of cm). Let us consider theexample of a decoration sheet for IMD (In-mould Decorating). Twoopposing advantages are desired. The first is that it is necessary tohave a material that is malleable when hot (between T_(g) and T_(m)) sothat it can undergo deep thermoforming (pronounced 3rd dimension or highrelief). The second is that, after the object has been manufactured byIMD, it is necessary to have a surface that is sufficiently hard andtough to withstand mechanical attack such as scratching, notching,impact, etc. In the prior art, it is necessary to have a range of sheetsor films, some being more thermoformable but less resistant tomechanical attack (or requiring an additional crosslinking operation orthe addition of a protective varnish), the others having a surface thatis harder and more resistant but only able to be thermoformed lessdeeply (in low relief). In contrast, the microcrystalline polyamide ofthe invention makes it possible to have both advantages at the sametime. This is because it is particularly thermoformable, beingparticularly soft/malleable in the temperature region between its T_(g)and its T_(m), during its manufacture, while still being thereafter,during its use at T<T_(g), sufficiently hard, rigid and tough to providevery good resistance to mechanical attack of the scratching, cutting andimpact type. This double advantage is provided by the microcrystallinecharacter and the low degree of crystallinity of the semicrystallineproduct, which provides a particularly large difference in rigidity (asmeasured by the flexural, tensile and/or shear modulus) between thetemperature region below T_(g) and the region between T_(g) and T_(m).

Injection moulding in the pseudo-liquid state below T_(m). Themicrocrystalline polyamide of the invention is advantageous forreproducing surface finishes in processing operations carried out in theliquid state, such as injection moulding. At first sight, it would seemthat injection moulding is a process carried out in the liquid state,and therefore above T_(m) and not between T_(g) and T_(m). However, inthe operation of injection moulding, over part of the time during whichit is being carried out, the skin of the object is in the solid stateand the core in the liquid state, the latter exerting a pressure on theskin against the surface of the mould. A not inconsiderable portion ofthe thickness is therefore in the solid state, in fact between T_(g) andT_(m), and subjected to a pressure coming from the core of the part.Under these circumstances, the microcrystalline polyamide of theinvention will also be better able to reproduce the surface texture ofthe mould than more conventional materials, such as amorphousthermoplastic polymer materials or “standard” non-transparentsemicrystalline polymer materials.

Thus, PA-11 No. 6 (T_(g)˜55° C. and T_(m)˜188° C.), which therefore isliquid above about 188° C., reproduces the grained surface of the mouldmore faithfully than the materials below:

-   -   the semicrystalline PA-11 Rilsan BESN0 TL (T_(g)˜45° C. and        T_(m)˜188° C.), which therefore is liquid above about 188° C.,        reproduces the grained surface of the mould less faithfully than        PA-11 No. 6;    -   the amorphous PA termed PA-BMACM.T/BMACM.1/12 (Cristamid MS1700        from Atofina) with a T_(g) of about 170° C., which is therefore        liquid above about 170° C., poorly reproduces the grained        surface of the mould, as it solidifies too quickly on contact        with the cold wall (20° C.) of the mould. The situation is no        better if the mould is heated to 100° C.

Adhesion to a substrate. Better ability to adhere to a substratepossessing anfractuosities (i.e. having a relief sufficiently pronouncedfor points of attachment to be able to be created with another material)will be described. For example, the microcrystalline polyamide of theinvention can be pressed onto wood or fabric, below T_(m), underpressure and for a certain time, and can generate good adhesion to thissubstrate. (A conventional semicrystalline material will not adhere, orless strongly, or will require longer time, higher temperature or higherpressure). In comparison with the “double-sided visuo-tactile structurewith wood appearance & bonding on the lower face and a wood feel on theupper face” paragraph, and by analogy with the previous paragraph oninjection moulding in the liquid state, the temperature is partlybetween T_(g) and T_(m). In other words, our material is in a laminationprocess in which it is deposited in the melt state onto the coldsubstrate, but it is already partly cooled between T_(g) and T_(m) onthe cold substrate side, and therefore its malleability (between T_(g)and T_(m)) advantageously acts in its favour in order to create theas-desired adhesion to the substrate.

Glass-fibre-filled microcrystalline polyamide—surface appearance, feeland colour. Another example of an advantageous use of themicrocrystalline polyamide of the invention is the case of compositesand polymers filled with an isotropic mineral material (for examplecalcium carbonate) or anisotropic mineral material, such as fibre (forexample glass fibre or carbon fibre). To give an example, themicrocrystalline polyamide may contain 30% by weight of fillers such as,for example, glass fibres. This material loses its transparency,becoming opaque. This does not prevent the composition from having twoadvantages associated with its semicrystalline and microcrystallinecharacter and with its low degree of crystallinity. If such acomposition is moulded in a polished mould, the surface finish of theobject obtained will not have the roughness defects and unattractivenesscharacteristic of amorphous polymers or semicrystalline polymers with ahigh degree of crystallinity and filled with glass fibre, these defectsresulting from the random presence of fibres on the surface of the part.By contrast, the polished surface finish of the mould will be betterreproduced with our composition and the object will appear smoother andmore uniform. Our material, being more malleable, mobile and solidifyingmore slowly, will allow better arrangement of the fibre. Anotheradvantage is the colour rendering. Consider for example the compositioncomprising PA-11 No. 6 with 30 parts of glass fibre and 0.5 parts of agrey metallic pigment. The intrinsically transparent nature of ourmaterial, combined with the good surface appearance, will bring out thecolour and its metallic appearance very much better, like that which atransparent varnish would provide. Thus, a microcrystalline PA-11 filledwith 30 parts of glass fibre 0.5 parts of pigment may advantageouslyreplace a PA-6 filled with 30 parts of glass fibre and 0.5 parts ofpigment, and even PA-6 filled with 30 parts of glass fibre and thenpainted (which is expensive and often not very environmentallyfriendly). This applies for other, non-mineral, fillers, it beingunderstood that these fillers are not in the molten state duringmanufacture of the object, in other words their melting point isappreciably above that of our microcrystalline polyamide. These fillersmay for example be plant-derived fibres or wood. Typically, the mineralor plant-derived fillers are added to the material during a conventionalcompounding step. These fillers are typically dispersed fillers.However, this does not constitute a limitation, and composites of anyshape and any size may be considered.

Microcrystalline polyamide highly filled with mineral powder. To obtainobjects with a mineral appearance (of the granite or other stone type),it is possible to use an amorphous transparent polymer such as PMMA andto fill it with 30-80% of mineral powder or filler. It is then given a3-dimensional shape in order to produce a finished object therefrom, forexample a kitchen sink. By using microcrystalline PA instead of PMMA itwill be possible to obtain better formability (deep 3-dimensional shape)and it will also be possible to obtain better texturizing(scratch-resistant embossing type, structurizing type, facilitating theflow of water, pleasant feel type and reproducing more faithfully thatof stone) and to do so much more easily. Of course, the polyamide highlyfilled with mineral powder or with pigment is no longer transparent, butits intrinsic transparency means that the colour of the mineral filleror of the pigments comes out more strikingly and attractively.

Microcrystalline Polyamide with Scratch-Resistant and Wear-ResistantTexturization.

To obtain scratch-resistant and wear-resistant objects, the intrinsicresistance of the material is not the sole factor. Suitable surfacetexturing is also beneficial, as is known. Because the microcrystallinePA has a malleable character (but is molten between its. T_(g) and itsT_(m)), we are able to use, as texturizing surface, a loose fabric or amesh. This will be impressed into our material and will leave a surfacein negative, that is to say a surface consisting of bumps and grooves.This surface is particularly resistant to wear. Similar effects may beobtained with a paper or an embossed textile. One particularlyadvantageous situation is that in which glossy bumps and matt valleyswith a soft feel are generated. Good visual wear resistance is thencombined with a soft feel.

Repairability when hot. Another advantage of the polyamide of theinvention, the advantage again being attributable to its semicrystallineand microcrystalline character and to its low (but not too low however)degree of crystallinity, is its ability to be repaired. This is because,should there be a scratch or blemish, it is possible to flame brush itssurface and, through the action of the heat, the scratch or blemish willheal or be filled in, without thereby all of the object liquefying ordeforming prejudiciously. As an example illustrating the use of thisadvantage relating to compositions filled with a mineral material, weconsider a floor tile filled with 50 parts of calcium carbonate. Owingto the nature of our microcrystalline polymer, we will have theadvantage of being easily able to obtain the appearance and feel ofquarry stone or, on the contrary, the appearance and feel of polishedmarble (during the manufacture of the tile between T_(g) and T_(m)), theadvantage of benefiting from the high resistance to mechanical andchemical attack (during use of the object as a floor tile) and finallythe advantage of being able subsequently (after the object has been usedfor a long time) to repair any scratches by heating the tile using theflame of a torch.

Ability to undergo hot reforming. In the previous paragraph weillustrated the ability to repair a small defect of the scratch type. Wewill now illustrate the ability to correct a large dimensional defect.Let us consider an object made from our microcrystalline PA, for examplea smooth sheet 600 microns in thickness decorated by sublimationdecoration, but exhibiting a tiling defect, that is to say having aconcave shape and a tendency to curl up. To correct this problem, it issufficient to place the sheet in a forming device, that is to saybetween two flat polished metal plates, ensuring that the upper plate issufficiently heavy. The assembly is then heated to a temperature betweenT_(g) and T_(m), for example 80° C., for 8 hours. After cooling, thesheet is removed and observed now to be flat—it is therefore correctedand no longer has the dimensional defect. This correction is notfeasible, or only partly feasible, if the material is a conventionalsemicrystalline polymer—on removing the sheet from the forming device,it will resume, at least partially, its original concave appearance.This return to the original concave state will continue with time orwith increasing temperature. With an amorphous polymer, the situation iseven more disadvantageous. Above T_(g), the polymer is liquid, it cannotpreserve the integrity of its decoration and it will flow out via theedges between the two plates of the forming device, while below T_(g) itis much too rigid and will not maintain its concave shape.

Complex Decorated Object Illustrating Various Advantages of theMicrocrystalline PA of the Invention.

Manufacturing step 1: the transparent sheet. The microcrystallinepolyamide is extruded and calendered in sheet form. The thickness mayfor example be between 200 and 800 μm. This polymer material has theadvantage of being easy to extrude (it crystallizes and solidifies lessquickly on the calendering rolls than a standard semicrystallinepolyamide) and of being transparent (a standard PA-11 for example beingmerely translucent). It is possible to use PA-11 No. 6 for thismaterial.

Manufacturing step 2: sublimation decoration. A coloured decoration(supported on a sheet of paper) and bearing a logo and an inscription inletters and numerals is imparted to the sheet during a sublimationprocess (the sheet bearing the decoration is pressed against the sheetof microcrystalline polyamide and then heated so that the dyes sublimeand pass into the microcrystalline polyamide). This sublimation isusually carried out at around 170° C. for 2 minutes and at 2 bar. Thisdecoration does not cover all of the sheet—there remain undecorated, andtherefore colourless and transparent, areas. The sublimed decoration isplaced on the lower face of the transparent sheet. It will therefore beprotected and the thickness of transparent material that covers itenhances its aesthetic appearance (varnished appearance). With astandard semicrystalline PA-11, it is not advantageous to place thedecoration on the lower face, since this material is insufficientlytransparent for the decoration, seen from the upper face side, to beproperly rendered. With a transparent amorphous PA, the sublimationoperation is not possible below T_(g) (poor penetration of the sublimedpigments) nor above T_(g) (liquefaction of the sheet). Ourmicrocrystalline material is therefore advantageous.

Manufacturing step 3: thermoforming. The decorated microcrystallinepolyamide sheet is then thermoformed into the form of athree-dimensional object (for example car engine cover). Themicrocrystalline polyamide lends itself particularly well to this hotforming operation, between T_(g) and T_(m). In the case of PA-11 No. 6,the operation is carried out at about 170° C. for three minutes.

Manufacturing step 4: overmoulding and finishing. The decoratedthermoformed sheet is then placed in an injection mould, thenon-decorated face being against the mould wall. This mould wall, on theside facing the future face of the finished object, has a “brushed”-typefinish, that is to say it is textured by unidirectional scratches.However, at the centre of this mould wall there is a polished shiny areain the form of a logo. The mould is closed and a standardsemicrystalline polyamide (for example PA-12) pigmented metallic grey isthen injected. This polyamide (PA-12) is then overmoulded onto thedecorated internal face of the microcrystalline polyamide sheet over athickness of around 1 to 5 mm for example. On removal from the mould,the finished “engine cover” object is obtained. This object is decoratedboth visually and tactilely. The following areas of decoration may infact be observed:

-   -   an area of metallic grey colour with the appearance and feel of        brushed aluminium (corresponding to an area that is not        sublimation decorated);    -   in the middle of the above area, an area of metallic grey colour        with a polished appearance and feel, in the form of a logo;    -   various coloured areas corresponding to areas sublimation        decorated with dark and opaque colours;    -   various coloured and metalized areas corresponding to areas        sublimation decorated with light and translucent colours, and        therefore letting through the adjacent metallic pigmentation of        the injection-moulded polyamide (PA-12); and    -   various areas with a logo, letters and numerals, corresponding        to the areas thus sublimation decorated.

All these visual decorations are of course protected mechanically,physically and chemically by a thickness of our polymer material. It maytherefore be seen that our microcrystalline polyamide material isparticularly advantageous for obtaining complex and attractivevisuo-tactile decorations. It also allows greater freedom than othermaterials, such as amorphous polymers, semicrystalline polymers andpaints. Paint has the advantage of offering various types of feel (butonly one type at a time), but the disadvantage of being limited in termsof visual decoration and protection (letters, numerals, logos). Thesestandard polymers are themselves limited in terms of feel, althoughadvantageous in terms of visual decoration. The microcrystalline PAcombines all these advantages.

Examples Illustrating Various Processes that can be Used to Give OurMaterial a Texture and a Feel

We have already mentioned the IMD (In-mould decoration) process. We nowmention, again within the context of the process called thermoplasticinjection moulding, various process options for obtaining objects with afeel and a very elaborate and/or unprecedented texturing or a plastic.In general, we consider the injection moulding process in which a filmor sheet of our material (whether or not predecorated or pigmented) isplaced in the bottom of the mould into which mould a molten polymer isthen injected. Our material will warm up, from the heat provided by themolten polymer and by the heat of the mould, will go above its T_(g) andwill soften sufficiently to be capable of assuming the grain of thesurface of the mould without in any way melting, aided in this by thehigh pressure within the medium. We will now consider the possibleprocess variants.

The first inventive variant of the process is to insert, between themould and the film of our material, a paper or fabric texturizing sheet(or the like). This has the advantage of avoiding having to texturizethe metal of the injection mould, and of making it possible to changethe texturing very easily without changing mould.

As 2nd variant, it is also possible to use a film of our material thathas already been textured (in another operation, at another time) and touse it as texturizing surface for texturing another film of ourmaterial. It is therefore very easy to use another solid polymer, andadvantageously the same polymer, as texturizing surface. In other words,it is possible to imagine a metal mould with texturizing inserts made ofplastic (or any other solid material).

As 3rd variant, it is conceivable to place the texturizing surfaceelsewhere than in the injection mould, for example in a prior step. Wewill consider most particularly the inventive variant involving theprior step in which the film of our polymer material is manufactured.Our polymer is melted by an extrusion process and is sheeted out on achilled roll (“casting” process) or calendered between two chilled rolls(“calendering” process). Upon cooling, our material solidifies, butnevertheless firstly remains sufficiently warm and above its T_(g). Atthis moment it is laminated on a fabric or paper texturizing surface (orthe like) and subjected to pressure. It will then acquire the texture ofthis fabric or paper (or the like). Furthermore, the texturizing surfacewill also act as a protective film for our film. During the subsequenthot manufacturing steps that our film/texturizing surface assembly willundergo, whether a thermoforming operation, a coating operating, acompression moulding operation or an overmoulding operation (asdescribed in the first variants), the texturing of our film will notdisappear, but will be further enhanced. It is not essential totexturize during the final hot manufacturing step.

As 4th variant, and as we have already mentioned, we can usethermoplastic conversion processes, either individually or insuccession, such as extrusion-lamination, thermoforming, injectionmoulding with overmoulding.

As 5th inventive variant, we may also use thermosetting conversiontechniques. For example, we may line the bottom of a mould with a filmof our polymer material and then deposit and cure a thermosetting resin(with its impregnated glass fibre fabric).

As 6th inventive variant, we may use multilayer films or sheets, madefrom an upper (visible) layer of our microcrystalline material and froma lower layer of a second polymer (and if necessary a tie layer betweenthem). The benefit of this second polymer is to be able to better adhereto a 3rd material, typically a molten polymer (typically introducedduring a subsequent overmoulding step), the second polymer being of thesame nature as the third or else being compatible with and adherent toit. This may be illustrated with the “microcrystalline PA”/PEBA bilayerfilm (PEBA=polyether-block-amide, an elastomer; PA=polyamide). This filmis placed on the bottom of a shoe sole mould. Molten PEBA is theninjected. The adhesion between the molten polymer and the PEBA face ofthe film is excellent. As a variant, molten TPU (and not PEBA) is theninjected. The adhesion between the molten polymer and the PEBA face ofthe film is excellent. This is also illustrated by a “microcrystallinePA/anhydride-grafted polypropylene/polypropylene” trilayer film which isthen overmoulded with polypropylene. This is also illustrated by a“microcrystalline PA/ether-TPU” bilayer film which is then overmouldedwith ester-TPU or with PA6. The adhesion between the molten polymer andthe PEBA face of the film is excellent. As mentioned above, otherprocesses may be employed. To obtain a PEBA shoe sole, thereforepossessing the well-known advantages of PEBA (nerviness, elasticity) andalso possessing the visuo-tactile and endurance advantages ofmicrocrystalline polyamide, a microcrystalline PA/PEBA multilayer sheetmay be used alone, without overmoulding, by just thermoforming. Theratio of the PA thickness to the PEBA thickness will be adjustedaccording to the overall compromise of properties sought. Within thesame context, knowing that the combination of microcrystalline PA withPEBA elastomer is particularly advantageous in the sports field, blends(alloys or dry blends before processing) of microcrystalline PA and PEBAare particularly beneficial.

As 7th variant we consider a film or sheet in which a small quantity ofmetal pigments (or those with a metallic appearance, or with ametallizing visual capability) has been dispersed. The sheet remainsquite transparent. In a subsequent step, we overmould a polymer tintedlight blue. The final part will have a metallic blue appearance with abeautiful depthwise rendition. The transparent film lightly filled withmetal pigment gives a metallic appearance to the blue colour of thesubstrate. Moreover, the film will mask any defects frominjection-moulding the substrate, in particular defects in the flow anddispersion of the light blue pigment in the injection-moulded part. Thisis because it is difficult to obtain good colour distribution ininjection-moulded parts, whereas it is much easier to do so on anextruded film. In fact, it is also possible to consider, as anothervariant, the use of a coloured opaque film (the colour of theovermoulded substrate will therefore not be seen thereafter). In arather similar mariner, the microcrystalline polyamide sheet may itselfconsist of various layers (in particular made from this same PA). theupper layer being lightly pigmented by metal pigments, but neverthelesstransparent, and the lower layer being highly pigmented with a colour insuch a way as to be sufficiently opaque. This multilayer sheet will havean attractive metallic appearance, good depth and, owing to itssufficient opacity, will mask any defects in the substrate, which willthen be overmoulded (or undermoulded to be more precise). To accentuatethe lacquer and depth effect, it is even possible to envisage anadditional upper layer of completely transparent microcrystallinepolyamide.

In general, the texturing (and the resulting feel) may be obtained byany warm (T_(g)-T_(m)) process that generates sufficient pressure topress our material (which is solid) against the texturizing surface.Under these conditions, the nature of the microcrystalline polyamide,namely not liquid (otherwise it would stick too much) and not too stiff(otherwise it would not take the texturing), makes it possible to give apolymer material a feel hitherto impossible to obtain with knownplastics. It has therefore become possible as it were to “clone” thetactile (and visual) rendition of materials of completely differentnature, such as fabric, paper, leather, wood, plants, etc. Thisadvantage may also be combined with other advantages, such as visualdecorability and protection properties (wear resistance, impactresistance, UV resistance and chemical resistance). This combination ofadvantages thus makes it possible in the end (after the manufacturingand finishing steps utilizing the properties of microcrystallinepolyamides) to obtain objects of high quality, both perceived andactual. These objects may for example be interior or exterior parts fora vehicle, sports equipment parts, such as shoes and skis, domesticelectrical appliance parts, telephone parts, computer cases, furniture,flooring, etc.

Examples of Microcrystalline Compositions that can be Used in thePresent Invention.

Blends or alloys of polymers consisting predominantly of C9 and higherpolyamide monomers, produced at a high enough temperature such that theresulting polymer is sufficiently transparent. These alloys consist of,on the one hand, a sufficient quantity of crystalline polymer (forexample, polyamide-11) for the final alloy to have a melting point andan enthalpy of melting greater than 25 J/g and, on the other hand, asufficient quantity of amorphous polymer (for example the polymerIPDA.12) for the final alloy to have sufficient transparency:

-   -   PA-11+30% PA-BMACM.12    -   PA-11+30% PA-BMACM.14    -   PA-11+30% PA-BMACM.14/BMACM.10 (80/20 wt %)    -   PA-11+30% PA-BMACM.IA/12    -   PA-11+30% PA-BMACM.IA/IBMACM.TA/12    -   PA-11+30% PA-PACM.12    -   PA-11+30% PA-IPDA.12    -   PA-11+30% PA-IPDA.10/12 (80/20 wt %)    -   PA-11+20% PA-IPDA.10/12 (80/20 wt %)+15% PEBA-12    -   PA-11+30% PA-10.IA    -   PA-11+30% PA-10.IA/10.TA

Copolymers consisting predominantly of C9 and higher monomers with, onthe one hand, a sufficient quantity of crystalline monomer (for examplethe 11 monomer unit) for the final copolymer to have a melting point andan enthalpy of melting greater than 25 J/g and, on the other hand, asufficient quantity of amorphous monomer (for example the monomer unitIPD.10) for the final copolymer to be sufficiently transparent:

-   -   90/10 wt % coPA-11/IPDA.10    -   90/10 wt % coPA-11/IPDA.10.

Polyamide compositions essentially composed of C9 monomers with the bestchemical, UV and impact protection properties (least dimensionalvariations) are preferred. However, it is possible to use blends oralloys of polymers predominantly consisting of C9 and lower polyamidemonomers, produced at a sufficient temperature such that the resultingpolymer is sufficiently transparent. These alloys consist of, on the onehand, a sufficient quantity of crystalline polymer (for examplepolyamide-6) for the final alloy to have a melting point and an enthalpyof melting greater than 25 J/g and, on the other hand, a sufficientquantity of amorphous polymer (for example the polymer PA-6,IA) for thefinal alloy to have sufficient transparency:

-   -   PA-6,12+30% PA-IPDA,6/IPDA,10 (70/30 wt %)    -   PA-6+30% PA-6-3,TA    -   PA-6+30% PA-6,IA    -   PA-6+30% PA-6,IA/6,TA    -   PA-6+30% PA-IPDA,6    -   PA-6+30% PA-BMACM,6/6 (70/30 wt %)    -   coPA-6/6,6 (80/20 wt %)+30% PA-6,IA    -   coPA-6/6,10 (80/20 wt %)+30% PA-6,IA    -   coPA-6/12 (80/20 wt %)+30% PA-6,IA    -   coPA-6, TA/6,6+30% PA-6,IA.

Copolymers consisting predominantly of C9 and lower monomers with, onthe one hand, a sufficient quantity of crystalline monomer (for examplethe 6,6 monomer unit) for final copolymer to have a melting point and anenthalpy of melting greater than 25 J/g and, on the other hand, asufficient quantity of amorphous monomer (for example the monomer unitIPD,6) for the final copolymer to have sufficient transparency:

-   -   coPA-6/IPD,6    -   coPA-6,6/6,T/6,I,10.

Legend:

*See above in the text,*PEBA-12: a copolymer comprising PA-12 blocks of 5000 M _(n) and PTMGblocks of 650 M _(n) and an MFI of 4 to 10 (g/10 min at 235° C./1 kg).*The percentages are percentages by weight.*NB: by “crystalline” we mean semicrystalline (no polymer being actuallycompletely crystalline—however it is common practice to use the term“crystalline”).

1. A process for obtaining an object having all or part of its outersurface formed from a microcrystalline polyamide and having a particularsurface finish, comprising the step of manufacturing said object betweenthe T_(g) (glass transition temperature) and the T_(m) (melting point)of said microcrystalline polyamide; wherein the transparency of themicrocrystalline polyamide is such that the light transmission at 560 nmon a polished object 1 mm in thickness is greater than 80%, thetransparency being measured on the object obtained by standardprocessing methods, such as injection moulding and sheetextrusion/calendering.
 2. The process according to claim 1, in which thetransparency of the microcrystalline polyamide is greater than 88%. 3.The process according to claim 1, wherein the microcrystalline polyamideis such that its degree of crystallinity is greater than 10% and lessthan 30% (1st DSC heating according to ISO 11357 at 40° C./min) and theenthalpy of melting is greater than 25.1/g and less than 75 J/g (1st DSCheating according to ISO 11357 at 40° C./min).
 4. The process accordingto claim 1, wherein the microcrystalline polyamide is such that itsT_(g) (glass transition temperature) is between 40° C. and 90° C. andits T_(m) (melting point) is between 150° C. and 200° C.
 5. The processaccording to claim 1, wherein the microcrystalline polyamide is suchthat it results from the chain-linking of monomers such that 50% ormore, by weight, of these monomers are ≧C9 monomers (i.e. having anumber of carbon atoms equal to 9 or higher).
 6. The process accordingto claim 1, wherein the microcrystalline polyamide also denotescopolyamides, compositions predominantly based on the latter or those inwhich the microcrystalline polyamide is the matrix constituent.
 7. Theprocess according to claim 6, in which the microcrystalline polyamidecompositions may be alloys, blends, composites, compositions thatinclude plasticizers, stabilizers, pigments or dyes, mineral fillers,and other miscible polymers that are compatible or are made compatibleby a third component.
 8. The process according to claim 1, wherein themicrocrystalline polyamide is a transparent composition comprising, byweight, the total being 100%: 5 to 40% of an amorphous polyamide (B)that results essentially from the condensation: either of at least onediamine chosen from cycloaliphatic diamines and aliphatic diamines andof at least one diacid, chosen from cycloaliphatic diacids and aliphaticdiacids, at least one of these diamines or diacid units beingcycloaliphatic, or of a cycloaliphatic α,Ω-aminocarboxylic acid, or of acombination of these two possibilities, and optionally of at least onemonomer chosen from α,Ω-aminocarboxylic acids or the possiblecorresponding lactams, aliphatic diacids and aliphatic diamines; 0 to40% of a flexible polyamide (C) chosen from copolymers having polyamideblocks and polyether blocks, and copolyamides; 0 to 20% of acompatibilizer (D) for (A) and (B); 0 to 40% of flexible modifier (M);with the condition that (C)+(D)+(M) is between 0 and 50%; the balance to100% of a semicrystalline polyamide (A).
 9. The process according toclaim 1, wherein the microcrystalline polyamide is a transparentcomposition comprising, by weight, the total being 100%: 5 to 40% of anamorphous polyamide (B) that results essentially from the condensationof at least one optionally cycloaliphatic diamine, of at least onearomatic diacid and optionally of at least one monomer chosen from:α-Ω-aminocarboxylic acids, aliphatic diacids, aliphatic diamines; 0 to40% of a flexible polymer (C) chosen from copolymers having polyamideblocks and polyether blocks, and copolyamides; 0 to 20% of acompatibilizer (D) for (A) and (B), (C)+(D) is between 2 and 50%; withthe condition that (B)+(C)+(D) is not less than 30%, the balance to 100%of a semicrystalline polyamide (A).
 10. The process according to claim8, in which the polyamide (A) is PA-11 or PA-12.
 11. An object obtainedby the process of claim 1, and manufactured from this microcrystallinepolyamide or objects having all or part of their external surfaceconsisting of this microcrystalline polyamide exhibiting a particularsurface finish.
 12. The process according to claim 1, wherein themicrocrystalline polyamide is combined, if necessary by means of a tie,with a layer of a second polymer.
 13. The process according to claim 12,in which said second polymer is of the same nature as, or is capable ofadhering to, a 3rd polymer, preferably molten, which will besubsequently (or elsewhere) combined with it, most particularly duringan overmoulding step.
 14. The process according to claim 13, in whichthe second polymer is chosen from PEBAs, TPUs, PEs, PPs, ABSs, PCs, 610,612, 11, 12 PAs, C9 PA and copolyamides, PA alloys, polyphthalamides,transparent amorphous PAs and PMMAs.
 15. The process according to claim1, in which the microcrystalline polyamide is such that its enthalpy isgreater than 25 J/g (1st DSC heating according to ISO 11357 at 40°C./min) and the transparency of the microcrystalline polyamide is suchthat the light transmission at 560 nm on a polished object 1 mm inthickness is greater than 80%, the transparency being measured on theobject obtained by the usual processing methods, such as injectionmoulding, sheet extrusion and calendering.
 16. The process according toclaim 1, wherein a small quantity of pigment, preferably of metallicappearance, is dispersed in the microcrystalline polymer in such a waythat it nevertheless remains transparent.